1. Field of the Invention
The invention relates generally to methods of treating heart disease and, more specifically, to a method of using RNAi to reduce phospholamban (PLB) for the treatment of chronic heart failure, including delivery by adeno-associated virus (AAV), a targeting AAV9 vector, and a method of diagnosing susceptibility to treatment by RNAi for chronic heart failure.
2. Background Information
Heart failure currently affects more than two million Americans and its economic and human toll will continue to increase as the population ages. Congestive heart failure is the most common inpatient diagnosis for patients 65 years old and older, with more than 400,000 new cases reported each year. The prognosis is poor, with 60% mortality within 5 years, and 23-52% of deaths attributable to fatal arrhythmias (sudden cardiac death; SCD).
Heart failure is an inability to match cardiac output to physiological demand. Heart failure is therefore not a specific disease, but a syndrome that represents the end-point of most cardiac diseases, including ischemic heart disease, cardiomyopathies (dilative, restrictive, or hypertrophic), valvular heart diseases and chronic hypertension and diabetes. In addition, the symptoms of heart failure can also present acutely (i.e., acute heart failure, or cardiogenic shock) in instances as acute myocardial infarction, post cardiac surgery (stunning, hybernation) or post re-vascularization therapy (i.e. reperfusion injury, post thrombolysis, percutaneous transluminal coronary angioplasty or coronary artery by-pass grafting).
Depressed contractility is a central feature of congestive heart failure, and the sarcoplasmic reticulum (SR), which stores calcium in cardiomyocytes, plays a key role in cardiac contractility as well as in the coupling of excitation and contraction. The development of contractile force depends on the amount of Ca2+ accumulated in the SR. An increase in abundance of the sarcoplasmic reticulum calcium ATPase (SERCAa) or increase in the phosphorylation of phospholamban (PLB) and/or decrease in PLB abundance may contribute to an increase in Ca2+ uptake by the SR, thereby enhancing the contractility of cardiomyocytes.
PLB is a 53 amino acid, muscle-specific phosphoprotein. Dephosphorylated PLB binds with SERCA2a and regulates the amount of calcium that enters into the SR in cardiac muscle. When phosphorylated by protein kinase A, PLB inhibition of SERCA2a is relived, increasing calcium flux into the SR and enhancing contractility of the muscle.
Myocardial gene therapy can be used for the treatment of a number of cardiovascular diseases, including ischemic cardiomyopathies, congestive heart failure, and malignant arrhythmias. A useful vector for myocardial gene delivery would allow efficient and stable transduction of cardiomyocytes with a variety of transgenes after either direct intramyocardial injection or infusion into the coronary arteries or sinuses. For example, plasmid DNA vectors injected directly into the left ventricular myocardium have been expressed for 6 months by cardiomyocytes adjacent to the area of injection. However, the therapeutic usefulness of this approach has been limited by the low efficiency of cardiomyocyte transduction (0.1% to 1.0% of cardiomyocytes in the area of injection).
Both intramyocardial injection and intracoronary infusion of replication-defective adenovirus (RDAd) vectors have been used to efficiently transduce cardiomyocytes in rodents, rabbits, and pigs in vivo. However, the feasibility of adenovirus-mediated gene transfer has been limited by immune responses to viral and foreign transgene proteins, which cause significant myocardial inflammation, elimination of virus-transduced cells within 30 days of infection, and thereby result in transient recombinant gene expression in immunocompetent hosts.